Device for inspecting element substrates and method of inspection using this device

ABSTRACT

A light-emitting device is produced at a decreased cost by inspecting defects in the pixels in the step of fabrication. TFTs possessed by the pixels on the element substrate and TFTs possessed by the peripheral drive circuits are inspected by using the inspection device to detect defects in a step in a process for finishing the light-emitting device. This makes it possible to decrease the loss that results when the defective products are processed through up to the final step, and to improve the yield by repairing the defective products in a step of repairing.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a device for inspecting whether a pixelportion properly operates prior to forming an EL (electroluminescence)element in a light-emitting device in which the EL element is formed ona substrate and to a method of inspection. The EL (electroluminescent)devices referred to in this specification include triplet-based lightemission devices and/or singlet-based light emission devices, forexample. More particularly, the invention relates to a device forinspecting whether the pixel portion properly operates prior to formingan EL element in a light-emitting device that uses a semiconductorelement (using a thin semiconductor film), to a method of inspection, toa method of fabricating the light-emitting device that incorporates theinspection method in one of the fabrication steps and to thelight-emitting device fabricated by using the above fabrication method.

[0003] The EL element according to this invention has a structure inwhich an EL layer is sandwiched between a pair of electrodes. The ELlayer stands for a layer containing an organic compound that emitsfluorescent light or phosphorescent light upon the application of anelectric field.

[0004] The light-emitting device to be inspected by the inspectiondevice of this invention stands for an image display device or alight-emitting device using an EL element. Further, the light-emittingdevice encompasses all of those modules in which a connector such as ananisotropic electrically conducting film (FPC: flexible printedcircuit), a TAB (tape automated bonding) tape or a TCP (tape carrierpackage) is attached to the EL element, modules in which a printedwiring board is provided at an end of the TAB tape or the TCP, or themodules in which an IC (integrated circuit) is directly mounted on theEL element by a COG (chip-on-glass) system.

[0005] 2. Description of the Prior Art

[0006] In recent years, technology has been greatly advanced concerningforming TFTs (thin-film transistors) on a substrate, and attempts havebeen made to apply the technology to the active matrix display devices(light-emitting devices). In particular, the TFT using a polysiliconfilm exhibits a field-effect mobility (also called mobility) which ishigher than that of the conventional TFT using an amorphous siliconfilm, and makes it possible to accomplish a high-speed operation. Thismakes it possible to control the pixels that had been controlled by adrive circuit outside the substrate by using a drive circuit formed onthe same substrate as the pixels.

[0007] In the active matrix light-emitting device, various circuits andelements are formed on the same substrate to obtain various advantagessuch as decreasing the cost of production, decreasing the size of theelectro-optical device, increasing the yield and decreasing thethroughput.

[0008] Further, study has been vigorously forwarded concerning theactive matrix light-emitting device (inclusive of EL display) having anEL element as a self-light-emitting element. The light-emitting deviceis also called an organic EL display (OELD) or an organic light-emittingdiode (OLED).

[0009] The EL element possessed by the light-emitting device has astructure in which the EL layer of an organic compound is sandwichedbetween a pair of electrodes (cathode and anode). Here, however, the ELlayer usually has a laminated-layer structure. A representative examplemay be a laminated-layer structure of “positive hole-transportinglayer/light-emitting layer/electron-transporting layer” proposed by Tanget al. of Codak Eastman Co. This structure features a very highlight-emitting efficiency. Most of the light-emitting devices that havenow been studied and developed are employing this structure.

[0010] There may be further employed a structure in which the positivehole-injection layer/positive hole-transporting layer/light-emittinglayer/electron-transporting layer or positive hole-injectionlayer/positive hole-transporting layer/light-emittinglayer/electron-transporting layer/electron injection layer are laminatedon the anode in order mentioned. The light-emitting layer may be dopedwith a fluorescent pigment.

[0011] In this specification, the layers provided between the cathodeand the anode are all called EL layers. Therefore, the above positivehole-injection layer, positive hole-transporting layer, light-emittinglayer, electron-transporting layer and electron injection layer allpertain to the EL layers.

[0012] A predetermined voltage is applied from a pair of electrodes tothe EL layer of the above structure, whereby the carriers are recombinedin the light-emitting layer to emit light. In this specification, alight-emitting element formed by the anode, EL layer and cathode iscalled EL element.

[0013] The EL layer possessed by the EL element is deteriorated by heat,light, moisture and oxygen. In fabricating the active matrixlight-emitting device, therefore, the EL element is formed after thewiring and TFT are formed in the pixel portion.

[0014] After the EL element is formed, the substrate (EL panel) on whichthe EL element is provided and a cover member are stuck and sealed(packaged) together with a sealing member in a manner that the ELelement is not exposed to the external air.

[0015] After the air-tightness is heightened by the treatment such aspackaging, a connector (FPC, TAB, etc.) is attached for connecting theterminals drawn from the element or the circuit formed on the substrateto the external signal terminals, thereby to complete the active matrixlight-emitting device.

[0016] In the active matrix light-emitting device, however, apredetermined voltage (current flowing into the EL layer) applied to theEL layer from the pair of electrodes of the EL element is controlled bya transistor provided in each of the pixels. Therefore, if some troubleoccurs such as failure of the function of the transistor in the pixelportion, break or short-circuiting of the wiring, the predeterminedvoltage (current) is no longer applied to the EL layer possessed by theEL element. In such a case, the pixel no longer displays a desiredgradation.

[0017] Even when the wiring or the transistor for controlling theemission of light from the EL element is defective in the pixel portion,however, it is not possible to make sure the presence of the defectuntil the light-emitting device is completed and is really used to makea display. In order to make a distinction from the acceptable productsby inspection, therefore, the EL element must be completed though it mayinclude a pixel portion that does not serve as a completed product, thepackaging must be effected, and the connector must be attached tocomplete it as the light-emitting device. In this case, the step offorming the EL element, the step of packaging and the step of attachingthe connector are wasted, resulting in a loss of time and cost. Evenwhen the EL panel is formed by using a multi-chamfered substrate, thestep of packaging and the step of attaching the connector are wasted,similarly, resulting in the loss of time and cost.

[0018] In the active matrix liquid crystal displays that aremass-produced earlier than the active matrix light-emitting devices, ithas been done to form the wiring and TFT in the pixel portion prior tocompleting the liquid crystal display by introducing the liquid crystalsinto between the two substrates, to electrically charge the capacitorspossessed by the pixels, and to measure the amount of electric chargefor each of the pixels to make sure the presence of defects in the pixelportions.

[0019] In the active matrix light-emitting devices, however, not lessthan two TFTs are generally included in each pixel. One electrode (pixelelectrode) and the capacitor in the EL element are often connectedtogether with the transistors sandwiched therebetween. In this case,measurement of the amount of electric charge stored in the capacitordoes not help make sure if the wiring and transistor connected betweenthe capacitor and the pixel electrode are defective. In the case of thelight-emitting device, further, an electric current must be supplied tothe EL element and, hence, it is necessary to measure the electriccurrent that flows.

[0020] It has been urged to establish the method of inspecting whetherthe wiring and transistor in the pixel portion are defective or, inother words, whether a predetermined voltage can be applied (or, whethera predetermined current can be supplied) to the pixel electrode of theEL element of each pixel prior to completing the light-emitting devicein a process toward mass-producing the active matrix light-emittingdevices.

SUMMARY OF THE INVENTION

[0021] The inspection method utilizing electromagnetic waves disclosedin this specification inspects any defect in the semiconductor elementformed on the element substrate and in the pixels and wirings formedlike a matrix which are connected to the semiconductor element.

[0022] In this specification, the element substrate refers to the one onwhich there are formed the pixel electrodes connected to thesemiconductor elements among the pixels that are independently formed inthe pixel portion after the wirings and the semiconductor elements havebeen formed on the substrate. The semiconductor element stands for anelement which, by itself or in a plural number, constitutes a switchingfunction of a semiconductor material, as represented by a transistorand, particularly, by a field-effect transistor, typically MOS (metaloxide semiconductor) transistor or a thin-film transistor (TFT).Accordingly, both the semiconductor substrate on which the MOStransistor is formed and the substrate on which the TFT is formedpertain to the element substrates.

[0023] Among the wirings possessed by the pixel portion, the gate signallines are successively selected to successively input the signals havingthe same potential to the source signal lines in a state where all ofthe current feed lines are maintained at the same potential, in order tosuccessively select all of the pixels. In this specification, the pixelthat is selected means that a video signal is Input to the source signalline possessed by the pixel in a state where the gate signal linepossessed by the pixel is selected.

[0024] Further, an opposing detector substrate is provided on theelement substrate, and electromagnetic waves (preferably, an X-rays) areradiated from an electromagnetic wave source 101 to a gas between theopposing detector substrate 102 and the element substrate 103 as shownin FIG. 1(A). The electromagnetic wave source is the one capable ofgenerating electromagnetic waves. When the electromagnetic waves aregenerated, a gas (air in this case) is ionized due to theelectromagnetic waves, whereby ions are generated and an electric pathis established along which a current flows. In this specification, theopposing detector substrate stands for the one on which is formed anelectrode through which a current flows into the pixel electrodepossessed by the pixel on the element substrate. The electrode formed onthe opposing detector substrate is called opposing detector electrode.Further, a current-flowing state stands for the one in which the currentflowing into the pixel electrode of the element substrate, flows intothe opposing detector electrode of the opposing detector substrate.

[0025] When a pixel is selected on the element substrate 103, theselected pixel is connected to the opposing detector substrate 102. Thatis, upon successively selecting the pixels on the element substrate, thepixels can be electrically connected to the opposing detector substrate102 corresponding thereto. In detecting the current flowing into aparticular pixel on the element substrate as shown in FIG. 1(A), aposition at where the current flowing into the element substrate can bemore correctly measured, is called corresponding position. To providethe opposing detector substrate at a position corresponding to theelement substrate, the element substrate or the opposing detectorsubstrate must be so moved that the distance becomes the shortestbetween the pixel and the opposing detector electrode.

[0026] In this case, the current flowing into the opposing detectorsubstrate 102 can be measured by an ammeter 123 connected to theopposing detector substrate 102. That is, the current measured here isdue to the video signal input to the selected pixel of the elementsubstrate 103. Upon evaluating whether the measured current is lyingwithin a predetermined range, it is allowed to inspect whether thewirings and the transistors possessed by the pixels are defective.

[0027] When a pixel is selected and a current flowing into the pixelelectrode or into the electrically conducting film that serves as thepixel electrode lies outside the predetermined range, it can be regardedthat the transistor possessed by the pixel is not normally working orthe wiring is broken or is short-circuited. On the other hand, when apixel is selected and a current flowing into the pixel electrode or intothe electrically conducting film serving as the pixel electrode lieswithin the predetermined range, it can be regarded that the transistorand the wiring possessed by the pixel are normally working.

[0028] The range of current in which it can be regarded that thetransistor and the wiring are normally working, can be suitably set by aperson who conducts the inspection. When the number of the pixels inwhich the defects are occurring (defective pixels) is not smaller than nin the pixel portion as a result of inspection, it is regarded that theelement substrate is defective. The number n of the defective pixelswith which the device can be regarded to be defective, can be suitablyset by the person who conducts the inspection.

[0029] An organic compound layer is formed on the electrode (pixelelectrode) that has been formed on the element substrate inspected bythe inspection method of the invention and in contact thereto, and anelectrode (opposing electrode) is formed on the above organic compoundlayer in contact thereto to complete the light-emitting device. It isthen made possible to distinguish whether the element substrate isacceptable or defective without the need of really effecting thedisplay.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a diagram illustrating an inspection device of thisinvention;

[0031]FIG. 2 is a diagram illustrating a pixel structure of the elementsubstrate and of the opposing detector substrate of this invention;

[0032] FIGS. 3(A) and 3(B) illustrate a method of evaluation relyingupon the inspection according to this invention;

[0033] FIGS. 4(A) to 4(C) are diagrams illustrating how to fabricate alight-emitting device;

[0034] FIGS. 5(A) to 5(C) are diagrams illustrating how to fabricate thelight-emitting device;

[0035] FIGS. 6(A) to and 6(B) are diagrams illustrating how to fabricatethe light-emitting device;

[0036]FIG. 7(A) is a top view of an element substrate inspectedaccording to this invention;

[0037]FIG. 7(B) is a circuit diagram of the element substrate accordingto this invention.

[0038]FIG. 8(A) is a top view of the opposing detector substrate usedfor the invention;

[0039]FIG. 8(B) is a circuit diagram of the element substrate accordingto this invention.

[0040]FIG. 9 is a diagram illustrating the inspection method of thisinvention;

[0041]FIG. 10 is a circuit diagram of pixels in the light-emittingdevice;

[0042]FIG. 11 is a diagram illustrating the constitution of the opposingdetector substrate of this invention;

[0043]FIG. 12 is a diagram illustrating the constitution of the opposingdetector substrate of this invention;

[0044]FIG. 13 shows electric appliances using the light-emitting device;

[0045]FIG. 14 shows electric appliances using the light-emitting device;

[0046]FIG. 15 shows a light-emitting device inspected by the inspectionmethod of this invention; and

[0047] FIGS. 16(A) and 16(B) show light-emitting devices inspected bythe inspection method of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] The inspection device and the method of inspecting the elementsubstrate by using the inspection device according to the invention willnow be described with reference to FIG. 1. In this invention, thetransistor used for the light-emitting device may be either a MOStransistor or a thin-film transistor (hereinafter referred to as TFT).In the case of the TFT, further, there is no need of imposing limitationon the structure, and there may be used a TFT of a structure such as ofthe planar type or of the inverse stagger type. Further, the drivecircuit for the light-emitting device used in the invention may be aknown one.

[0049] When the inspection method of the invention is used for thelight-emitting device having an EL element, the element structure of theEL element and the EL material may comply with those of known ones.

[0050] In this specification, the inspection device refers to the oneincluding the source 101 of electromagnetic waves and the opposingdetector substrate 102 in combination. Here, however, the opposingdetector substrate 102 shown is an example of the invention, and is inno way limited to the one of a shape shown in FIG. 1(A). The opposingdetector substrates of other shapes will be described in detail in theworking examples in the specification.

[0051] The source 101 of electromagnetic waves is connected to a powersource 104. When a high voltage of several kilovolts is applied from thepower source 104 to two pieces of electrodes in the source 101 ofelectromagnetic waves, the electrons generated by the cathode impingeupon the anode to generate electromagnetic waves. In this invention, itis desired to use an X-ray or a soft X-ray having a wavelength of from0.01 to 100 nm. It is, however, also allowable to use electromagneticwaves that are capable of ionizing a gas existing between the opposingdetector substrate and the element substrate, if such electromagneticwaves are available.

[0052] The electromagnetic waves, in general, exhibit a photo-ionizationfunction. The principle is such that upon irradiating stable atoms andmolecules with electromagnetic waves, electrons in the atoms and in themolecules are sprung out, and the atoms and molecules assume thepositive (+) polarity since they are lacking electrons.

[0053] The electrons that are sprung out further attack other stableatoms and molecules to generate atoms or molecules having the negative(−) polarity.

[0054] As a result, atoms and molecules that are ionized into thepositive polarity and the negative polarity are present in the gasirradiated with electromagnetic waves. In this invention, therefore, theelement substrate 103 and the opposing detector substrate 102 areoverlapped as shown in FIG. 1(A) and are irradiated with electromagneticwaves from the source 101 of electromagnetic waves, so that the gaspresent between the element substrate 103 and the opposing detectorsubstrate 102 is irradiated with the electromagnetic waves. At thismoment, the gas (air) is ionized with electromagnetic waves, and anelectric passage of ions can be formed between the element substrate 103and the opposing detector substrate 102. The gas referred to here is theair. It is, however, also allowable to use a gas that is subject to bemore ionized. It is further desired that the distance between theopposing detector substrate 102 and the element substrate 103 is asclose as possible. Concretely speaking, it is desired that the distancebetween the opposing detector substrate 102 and the element substrate103 is not larger than 500 μm.

[0055] On the element substrate 103 are formed plural pixels in the formof a matrix. Further, the element substrate 103 is connected to thedrive circuit (A) 107. The drive circuit (A) 107 includes a drivecircuit of the gate side and a drive circuit of the source side. Asshown in FIG. 1(A), for example, a pixel 105 is selected when aselection signal is input to the pixel 105 from the drive circuit of thegate side. The selection signal referred to here stands for a signalthat opens the gate electrode when a signal is input to the gateelectrode connected to the gate line. A state where the gate electrodepossessed by the pixel is opened by the selection signal is referred toas that the pixel is selected. When the pixel 105 is selected and avideo signal is input thereto from the drive circuit of the source side,a current flows into the pixel electrode of the pixel 105 on the elementsubstrate 103. The current further flows into opposing portions 106formed on the opposing detector substrate 102 passing through the gasionized by electromagnetic waves. In this specification, the opposingportions 106 are the ones formed like a matrix on the opposing detectorsubstrate 102 being corresponded to the pixels 105 formed on the elementsubstrate 103. On each opposing portion, there are formed an opposingdetector electrode into which a current flows from the element substrate103 and an inspection TFT 120 connected to the opposing detectorelectrode. In this specification, the inspection TFT 120 stands for aTFT which is capable of flowing a current from the selected pixelelectrode on the element substrate 103 through the opposing detectorelectrode when the gate electrode is opened by a selection signal inputfrom a drive circuit (B) 108 connected to the opposing detectorsubstrate 102.

[0056]FIG. 1(B) is a diagram illustrating, on an enlarged scale, thepixels 105 formed like a matrix on the element substrate 103. Here,though the TFT is exemplified as a transistor, it is also allowable touse a MOS transistor. Referring to FIG. 1(B), the element substrate 103for effecting the inspection includes a drive TFT formed on an insulatorand TFTs (switching TFT and current control TFT) in the pixel portion.

[0057] In FIG. 1(B), reference numeral 110 denotes a switching TFT. Thegate electrode of the switching TFT 110 is connected to a gate signalline 111. The source region and drain region of the switching TFT 110are so connected that either one of them is connected to the sourcesignal line 112 and the other one is connected to the gate electrode ofthe current control TFT 113 and to a capacitor 114 possessed by thepixels.

[0058] The capacitor 114 is for holding a gate voltage of the currentcontrol TFT 113 (potential difference between the gate electrode and thesource region) when the switching TFT 110 has not been selected(off-state). Though the capacitor 114 is provided, here, the inventionis in no way limited to the above constitution only, and the capacitor114 may not be provided.

[0059] Further, the source region and drain region of the currentcontrol TFT 113 are so connected that either one of them is connected toa current feeder line 115 and the other one is connected to the pixelelectrode possessed by the pixel 105. When an electric passage is formedby the irradiation with electromagnetic waves, the pixel electrode isconnected to the source region of an inspection TFT (120 in FIG. 1(C))possessed by the opposing portion 106 on the opposing detector substrate102. The current feeder line 115 is connected to the capacitor 114.

[0060]FIG. 1(C) is a diagram illustrating, on an enlarged scale, theopposing portions 106 formed like a matrix on the opposing detectorsubstrate 102. An inspection TFT 120 is formed on each opposing portion,and the gate electrode is connected to a gate signal line 121 connectedto the drive circuit (B) 108. When a pixel on the element substrate 103is selected, an opposing portion 106 corresponding to the selected pixelon the substrate is selected by a selection signal from the drivecircuit (B) 108. The drain region of the inspection TFT 120 is connectedto a drain wiring 122 which is connected to an ammeter 123 on theexternal side.

[0061] The current feeder line 122 is served with a power sourcepotential which is produced by a power source constituted by an externalIC.

[0062] The switching TFT 110 and the current control TFT 113 may beeither of the n-channel type or the p-channel type. When the sourceregion or the drain region of the current control TFT 113 is connectedto the anode of an EL element that is formed later, however, it isdesired that the current control TFT 113 is of the p-channel type. Whenthe source region or the drain region of the current control TFT 113 isconnected to the cathode of the EL element, further, it is desired thatthe current control TFT 113 is of the n-channel type.

[0063] Further, the switching TFT 110 and the current control TFT 113may be of a multi-gate structure such as the double-gate structure orthe triple-gate structure in addition to the single-gate structure.

[0064] Next, FIGS. 2(A) and 2(B) illustrate the opposing detectorsubstrate 102 of the invention and the element substrate 103 to beinspected thereby. A pixel portion 201 shown in FIG. 2(A) is the one onwhich the pixels 105 shown in FIG. 1(B) are formed like a matrix. Thepixel portion 201 of FIG. 2(A) is provided with source signal lines (S1to Sx), current feeder lines (V1 to Vx) and gate signal lines (G1 toGy).

[0065] Here, the pixel 105 is a region including source signal line (S1to Sx), current feeder line (V1 to Vx) and gate signal line (G1 to Gy)each in a number of one.

[0066]FIG. 2(B) illustrates the opposing portions 106 formed like amatrix on the opposing detector substrate 102 according to theinvention. FIG. 2(B) shows gate signal lines (G1 to Gx). The opposingportions 106 are selected by signals from the gate signal lines (G1 toGx). The drain region of the inspecting TFT 120 in each opposing portion106 is connected to the current line (A) and is connected to an externalammeter 123.

[0067] That is, a current flows from a selected pixel on the elementsubstrate 103 through an electric passage into a selected opposingportion 106 on the opposing detector substrate 102, and is detected bythe ammeter 123. Either one or both of a stage securing the opposingdetector substrate and a stage securing the element substrate may beprovided with a positioning function, so that the distance becomes assmall as possible between the pixel 105 on the element substrate 103 andthe corresponding opposing portion 106 on the opposing detectorsubstrate 102.

[0068] Next, described below with reference to FIG. 3 is a method ofevaluating the switching TFTs 110 and current control TFTs 113 in thepixels 105 on the element substrate 103 by using the inspection methodof the invention.

[0069]FIG. 3(A) shows the pixels formed in the pixel portion 201 on theelement substrate 103 by way of X-Y coordinates (X, Y). Here, pixels ofX columns are formed on the surface of the paper in the transversedirection, and pixels of Y rows are formed on the surface of the paperin the longitudinal direction.

[0070] When the gate electrode of the pixel is selected, a video signalis input to the selected pixel from the source signal line electricallyconnected to the source signal line drive circuit. At this moment, thecurrent flows into the pixel electrode, input to the inspection TFT 120from the opposing detector electrode of the opposing detector substrate102 through the electric passage formed in the gas by the irradiationwith the electromagnetic waves and is, further, input to the ammeter 123connected on the external side passing through the drain wiring. Here,the current flowing between the selected pixel on the element substrate103 and the corresponding opposing portion is measured by the ammeter123. It is further allowable to form the ammeter 123 on the opposingdetector substrate 102.

[0071] In this embodiment, when the video signal contains “white” datairrespective of whether it may be in an analog form or in a digitalform, the current control TFT 113 is turned on. Therefore, the powersource potential is applied to the pixel electrode. As a result, acurrent flows from the pixel that has received the video signalcontaining “white” data to the opposing portion 106 on the opposingdetector substrate 102 and to the ammeter 123.

[0072] Conversely, when the video signal contains “black” data, thecurrent control TFT 113 formed on the element substrate 103 is turnedoff. Therefore, the power source potential is not applied to the pixelelectrode. As a result, a current flows from the pixel that has receivedthe video signal containing “black” data to the opposing portion 106 onthe opposing detector substrate 102 and to the ammeter 123, the currentbeing smaller than the current of when a video signal containing “white”data is input.

[0073] In the foregoing was described the case where both the switchingTFT 110 and the current control TFT 113 are normally working. Wheneither one of them is defective, however, it happens that a current thatshould flow fails to flow or a current that should not flow flows.

[0074] In this invention, therefore, a current of when the video signalis “black” and a current of when the video signal is “white” aremeasured in advance by using a pixel having a TFT that normally works touse them as reference data.

[0075] In this invention, further, the data are evaluated by using aratio of currents (ratio of white and black) that flow when the videosignals are white and black, respectively.

[0076]FIG. 3(B) illustrates the measured results represented by a ratioof standardized (normalized) white and black signals. In thisstandardization (normalization), 100 represents a sufficiently largeratio (contrast) of black and white by using the reference data. In thistable, the ordinate represents the ratio of white and black, and theabscissa represents the coordinate of pixels. Further, a reference isset for the ratio of white and black, and the device is regarded to beacceptable when the ratio of white and black is not smaller than 20 butis not larger than 100. That is, the hatched region of FIG. 3(B)represents references of acceptable devices.

[0077] However, when the ratio of white and black is lower than thereference value like a coordinate (1, 3), the device is judged to bedefective and is removed from the subsequent steps. The acceptablereference for the ratio of white and black may be set depending upon alevel that is required.

[0078] Upon evaluating the characteristics of the pixels relying uponthe above method, the defective products can be discovered at an earlytime. Accordingly, the defective products are removed from thesubsequent production process such as formation of EL element. Dependingupon the degree of defect, further, the device may be repaired through astep of repairing and may be returned back to the subsequent steps.Described below in detail in the following examples is a method ofcompleting the light-emitting device by forming an organic compoundlayer and a cathode (second electrode) on the pixel electrode (firstelectrode) after the step of inspecting the element substrate has beenfinished.

[0079] This makes it possible to decrease the loss that results when thedefective product is passed through up to the final step and to improvethe yield owing to the repairing.

EXAMPLE 1

[0080] A method of manufacturing a pixel TFT and TFTs of a drivercircuit (source signal line driver circuit, gate signal line drivercircuit and pixel selective signal line driver circuit) provided in theperiphery of a pixel portion is explained in this embodiment. Forsimplicity of the explanation, the CMOS circuit which is a basic unitconcerning with the driver circuit is illustrated.

[0081] First, as shown in FIG. 4A, a base film 5002 made of aninsulating film such as a silicon oxide film, a silicon nitride film, ora silicon oxynitride film is formed on a substrate 5001 made from glass,such as barium borosilicate glass or aluminum borosilicate glass,typically Corning Corp. #7059 glass or #1737 glass. For example, asilicon oxynitride film 5002 a manufactured from SiH₄, NH₃, and N₂O byplasma CVD is formed with a thickness of 10 to 200 nm (preferably from50 to 100 nm), and a hydrogenized silicon oxynitride film 5002 b with athickness of 50 to 200 nm (preferably between 100 and 150 nm),manufactured from SiH₄ and N₂O, is similarly formed and laminated. Thebase film 5002 with the two layer structure is shown in Embodiment 1,but the base film 5002 may also be formed as a single film or as alamination film in which two or more layers are laminated.

[0082] Island shape semiconductor layers 5003 to 5006 are formed ofcrystalline semiconductor film manufactured by using a laser crystallinemethod or a known thermal crystallization method with a semiconductorfilm having an amorphous structure. The thickness of the island shapesemiconductor layers 5003 to 5006 is set from 25 to 80 nm (preferablybetween 30 and 60 nm). There are no limitations on the crystallinesemiconductor film material but it is preferable to form the film from asemiconductor material such as silicon or a silicon germanium (SiGe)alloy.

[0083] A laser such as a pulse oscillation type or continuous emissiontype excimer laser, a YAG laser, or a YVO₄ laser can be used as a laserlight source in manufacturing the crystalline semiconductor film withthe laser crystallization method. A method of condensing laser lightemitted from a laser oscillator into a linear shape by an optical systemand then irradiating the light to the semiconductor film may be employedwhen these types of lasers are used. The crystallization conditions maybe suitably selected by the operator. However, the pulse oscillationfrequency is set to 300 Hz, and the laser energy density is set from 100to 400 mJ/cm² (typically between 200 and 300 mJ/cm²) when using theexcimer laser. Further, the second harmonic is utilized when using theYAG laser, the pulse oscillation frequency is set from 30 to 300 Hz, andthe laser energy density may be set from 300 to 600 mJ/cm² (typicallybetween 350 and 500 mJ/cm²). The laser light which has been condensedinto a linear shape with a width of 100 to 1000 mm, for example 400 mm,is then irradiated onto the entire surface of the substrate. This isperformed with an overlap ratio of 50 to 90% for the linear laser light.

[0084] A gate insulating film 5007 is formed covering the island shapesemiconductor layers 5003 to 5006. The gate insulating film 5007 isformed of an insulating film containing silicon having a thickness of 40to 150 nm by plasma CVD or sputtering. A 120 nm thick silicon oxynitridefilm is formed in Embodiment 1. The gate insulating film is not limitedto this type of silicon oxynitride film, of course, and other insulatingfilms containing silicon may also be used, in a single layer or in alamination structure. For example, when using a silicon oxide film, itcan be formed by plasma CVD with a mixture of TEOS (tetraethylorthosilicate) and O₂, at a reaction pressure of 40 Pa, with thesubstrate temperature set from 300 to 400° C., and by discharging at ahigh frequency (13.56 MHZ) electric power density of 0.5 to 0.8 W/cm².Good characteristics as a gate insulating film can be obtained bysubsequently performing thermal annealing, at between 400 and 500° C.,of the silicon oxide film thus manufactured.

[0085] A first conductive film 5008 and a second conductive film 5009are then formed on the gate insulating film 5007 in order to form gateelectrodes. The first conductive film 5008 is formed from Ta with athickness of 50 to 100 nm, and the second conductive film 5009 is formedby W with a thickness of 100 to 300 nm, in Embodiment 1.

[0086] The Ta film is formed by sputtering, and sputtering with a Tatarget is performed by using Ar. If appropriate amounts of Xe and Kr areadded to the Ar during sputtering, the internal stress of the Ta filmwill be relaxed, and film peeling can be prevented. The resistivity of αphase Ta film is on the order of 20 μΩcm, and it can be used in the gateelectrode, but the resistivity of β phase Ta film is on the order of 180μΩcm and it is unsuitable for the gate electrode. The α phase Ta filmcan easily be obtained if a tantalum nitride film, which possesses acrystal structure near that of α phase Ta, is formed with a thickness of10 to 50 nm as a base for Ta in order to form the α phase Ta film.

[0087] A W film is formed by sputtering with a W target. The W film canalso be formed by thermal CVD using tungsten hexafluoride (WF₆).Whichever is used, it is necessary to make the film become lowresistance in order to use it as the gate electrode, and it ispreferable that the resistivity of the W film be made equal to or lessthan 20 μΩcm. The resistivity can be lowered by enlarging the crystalsof the W film, but for cases in which there are many impurity elementssuch as oxygen within the W film, crystallization is inhibited, and thefilm becomes high resistance. A W target having a purity of 99.9999% isthus used in sputtering. In addition, the W film is formed whilesufficient care is taken in order that no impurities From within the gasphase are introduced at the time of film formation. Thus, a resistivityof 9 to 20 μΩcm can be achieved.

[0088] Note that, although the first conductive film 5008 is Ta and thesecond conductive film 5009 is W in Embodiment 1, the conductive filmsare not limited to these. Both the first conductive film 5008 and thesecond conductive film 5009 may also be formed from an element selectedfrom the group consisting of Ta, W, Ti, Mo, Al, and Cu, from an alloymaterial having one of these elements as its main constituent, or from achemical compound of these elements. Further, a semiconductor film,typically a polysilicon film, into which an impurity element such asphosphorous is doped may also be used. Examples of preferablecombinations other than that used in Embodiment 1 include: a combinationof the first conductive film 5008 formed from tantalum nitride (TaN) andthe second conductive film 5009 formed from W; a combination of thefirst conductive film formed from tantalum nitride (TaN) and the secondconductive film 5009 formed from Al; and a combination of the firstconductive film 5008 formed from tantalumnitride (TaN) and the secondconductive film 5009 formed from Cu.

[0089] A mask 5010 is formed next from resist, and a first etchingprocess is performed in order to form electrodes and wirings. An ICP(inductively coupled plasma) etching method is used in Embodiment 1. Agas mixture of CF₄ and Cl₂ is used as an etching gas, and a plasma isgenerated by applying a 500 W RF electric power (13.56 MHZ) to a coilshape electrode at 1 Pa. A 100 W RF electric power (13.56 MHZ) is alsoapplied to the substrate side (test piece stage), effectively applying anegative self-bias. The W film and the Ta film are both etched on thesame order when CF₄ and Cl₂ are combined.

[0090] Edge portions of the first conducting layer and the secondconducting layer are made into a tapered shape in accordance with theeffect of the bias voltage applied to the substrate side with the aboveetching conditions by using a suitable resist mask shape. The angle ofthe tapered portions is from 15 to 45°. The etching time may beincreased by approximately 10 to 20% in order to perform etching withoutany residue remaining on the gate insulating film. The selectivity of asilicon oxynitride film with respect to a W film is from 2 to 4(typically 3), and therefore approximately 20 to 50 nm of the exposedsurface of the silicon oxynitride film is etched by this over-etchingprocess. First shape conductive layers 5011 to 5016 (first conductivelayers 5011 a to 5016 a and second conductive layers 5011 b to 5016 b)composed of the first conducting layer and the second conducting layerare thus formed by the first etching process. Portions of the gateinsulating film 5007 not covered by the first shape conductive layers5011 to 5016 are etched on the order of 20 to 50 nm, forming thinnerregions. (See FIG. 4A.)

[0091] A first doping process is then performed, and an impurity elementwhich imparts n-type conductivity is added. Ion doping or ion injectionmay be performed as the doping method. Ion doping is performed atconditions in which the dosage is set to 1×10¹³ to 5×10¹⁴ atoms/cm², andan acceleration voltage is set between 60 and 100 keV. An elementresiding in group 15 of the periodic table, typically phosphorous (P) orarsenic (As), is used as the n-type conductivity imparting impurityelement. Phosphorous (P) is used here. The conductive layers 5011 to5015 become masks with respect to the n-type conductivity impartingimpurity element, and first impurity regions 5017 to 5025 are formed ina self-aligning manner. The impurity element which imparts n-typeconductivity is added to the first impurity regions 5017 to 5025 at aconcentration within a range of 1×10²⁰ and 1×10²¹ atoms/cm³. (See FIG.4B.)

[0092] A second etching process is performed without removing resistmask next as shown in FIG. 4C. The W film is etched selectively using amixture of CF₄, Cl₂, and O₂ is used as the etching gas. At that time, bythe second etching process, second shape conductive layers 5026 to 5031(first conductive layers 5026 a to 5031 a and second conductive layers5026 b to 5031 b) are formed. The gate insulating film 5007 isadditionally etched on the order of 20 to 50 nm, forming thinnerregions, in regions not covered by the second shape conductive layers5026 to 5031.

[0093] The etching reaction of the W film or the Ta film in accordancewith the mixed gas of CF₄ and Cl₂ can be estimated from the generatedradicals, or from the ion types and vapor pressures of the reactionproducts. Comparing the vapor pressures of W and Ta fluorides andchlorides, the W fluoride compound WF₆ is extremely high, and the vaporpressures of WCl₅, TaF₅, and TaCl₅ are of similar order. Therefore the Wfilm and the Ta film are both etched by the CF₄ and Cl₂ gas mixture.However, if a suitable quantity of O₂ is added to this gas mixture, CF₄and O₂ react, forming CO and F, and a large amount of F radicals or Fions are generated. As a result, the etching speed of the W film havinga high fluoride vapor pressure becomes high. On the other hand, even ifF increases, the etching speed of Ta does not relatively increase.Further, Ta is easily oxidized compared to W, and therefore the surfaceof Ta is oxidized by the addition of O₂. The etching speed of the Tafilm is further reduced because Ta oxides do not react with fluorine andchlorine. It therefore becomes possible to have a difference in etchingspeeds of the W film and the Ta film, and it becomes possible to makethe etching speed of the W film larger than that of the Ta film.

[0094] A second doping process is then performed as shown in FIG. 5A. Inthis case, an impurity element which imparts n-type conductivity isdoped under conditions of a lower dosage than that in the first dopingprocess, and at a higher acceleration voltage than that in the firstdoping process. For example, doping may be performed at an accelerationvoltage of 70 to 120 keV and with a dosage of 1×10¹³ atoms/cm², formingnew impurity regions inside the first impurity regions formed in theisland shape semiconductor layers of FIG. 4B. Doping is performed withthe first shape conductive layers 5026 to 5030 as masks with respect tothe impurity element, and doping is done such that the impurity elementis also added to regions below the first conductive layers 5026 a to5030 a. Third impurity regions 5032 to 5036 are formed. A concentrationof phosphorus (P) added to the third impurity region 5032 to 5036 isprovided with a gradual concentration gradient in accordance with a filmthickness of the taper portion of the first conductive layer 5026 a to5030 a. Further, in the semiconductor layer overlapping the taperportion of the first conductive layer 5026 a to 5030 a, from an endportion of the taper portion of the first conductive layer 5026 a to5030 a toward an inner side, the impurity concentration is more or lessreduced, however, the concentration stays to be substantially the samedegree.

[0095] As shown in FIG. 5B, a third etching process is performed. Thisis performed by using a reactive ion etching method (RIE method) with anetching gas of CHF₆. The tapered portions of the first conductive layers5026 a to 5031 a are partially etched, and the region in which the firstconductive layers overlap with the semiconductor layer is reduced by thethird etching process. Third shape conductive layers 5037 to 5042 (firstconductive layers 5037 a to 5042 a and second conductive layers 5037 bto 5042 b) are formed. At this point, regions of the gate insulatingfilm 5007, which are not covered with the third shape conductive layers5037 to 5042 are made thinner by about 20 to 50 nm by etching.

[0096] By the third etching process, third impurity regions 5032 a to5036 a, which overlap with the first conductive layers 5037 a to 5041 a,and second impurity regions 5032 b to 5236 b between the first impurityregions and the third impurity regions are formed in the third impurityregions.

[0097] Then, as shown in FIG. 5C, the third doping process is performedto form the fourth impurity regions 5043 to 5054, which have aconductivity type opposite to the first conductivity type, in theisland-like semiconductor layers 5004, 5006 forming p-channel TFTs. Thethird conductive layers 5038 b to 5041 b are used as masks to animpurity element, and the impurity regions are formed in a self-aligningmanner. At this time, the whole surfaces of the island-likesemiconductor layers 5003, 5005 and the wiring portion 5042, which formn-channel TFTs are covered with a resist mask 5200. Phosphorus is addedto the impurity regions 5043 to 5054 at different concentrations,respectively. The regions are formed by an ion doping method usingdiborane (B₂H₆) and the impurity concentration is made 2×10²⁰ to 2×10²¹atoms/cm³ in any of the regions.

[0098] By the steps up to this, the impurity regions are formed in therespective island-like semiconductor layers. The third shape conductivelayers 5043 to 5054 overlapping with the island-like semiconductorlayers function as gate electrodes. The conductive layer 5042 functionsas an island-like source signal line.

[0099] After the resist mask 5200 is removed, a step of activating theimpurity elements added in the respective island-like semiconductorlayers for the purpose of controlling the conductivity type isconducted. This step is carried out by a thermal annealing method usinga furnace annealing oven. In addition, a laser annealing method or arapid thermal annealing method (RTA method) can be applied. The thermalannealing method is performed in a nitrogen atmosphere having an oxygenconcentration of 1 ppm or less, preferably 0.1 ppm or less and at 400 to700° C., typically 500 to 600° C. In Embodiment 1, a heat treatment isconducted at 500° C. for 4 hours. However, in the case where a wiringmaterial used for the third conductive layers 5037 to 5042 is weak toheat, it is preferable that the activation is performed after aninterlayer insulating film (containing silicon as its main ingredient)is formed to protect the wiring line or the like.

[0100] Further, a heat treatment at 300 to 450° C. for 1 to 12 hours isconducted in an atmosphere containing hydrogen of 3 to 100%, and a stepof hydrogenating the island-like semiconductor layers is conducted. Thisstep is a step of terminating dangling bonds in the semiconductor layerby thermally excited hydrogen. As another means for hydrogenation,plasma hydrogenation (using hydrogen excited by plasma) may be carriedout.

[0101] Next, as shown in FIG. 6A, a first interlayer insulating film5055 made of an inorganic insulator material is formed. In thisembodiment, a first interlayer insulating film 5055 made of a siliconnitride film having a thickness of 100 to 200 nm is formed. A secondinterlayer insulating film 5056 made of an organic insulator materialformed thereon. Contact holes are then formed with respect to the firstinterlayer insulating film 5055, the second interlayer insulating film5056, and the gate insulating film 5007, respective wirings (includingconnection wirings and signal lines) 5057 to 5062, and 5064 are formedby patterning, and then, a pixel electrode 5063 that contacts with theconnection wiring 5062 is formed by patterning.

[0102] Next, the film made from organic resin is used for the secondinterlayer insulating film 5056. As the organic resin, polyimide,polyamide, acryl, BCB (benzocyclobutene) or the like can be used.Especially, since the second interlayer insulating film 5056 has ratherthe meaning of flattening, acryl excellent in flatness is desirable. InEmbodiment 1, an acryl film is formed to such a thickness that steppedportions formed by the TFTs can be adequately flattened. The thicknessis preferably made 1 to 5 μm (more preferably 2 to 4 μm).

[0103] In the formation of the contact holes, dry etching or wet etchingis used, and contact holes reaching the n-type impurity regions 5017,5018, 5021 and 5023 or the p-type impurity regions 5043 to 5054, acontact hole reaching the wiring 5042, a contact hole reaching the powersource supply line (not shown), and contact holes reaching the gateelectrodes (not shown) are formed, respectively.

[0104] Further, a lamination film of a three layer structure, in which a100 nm thick Ti film, a 300 nm thick aluminum film containing Ti, and a150 nm thick Ti film are formed in succession by sputtering, ispatterned into a desirable shape, and the resultant lamination film isused as the wirings (including connection wirings and signal lines) 5057to 5062, and 5064. Of course, other conductive films may be used.

[0105] In this example, further, an ITO film is formed maintaining athickness of 110 [nm] as a pixel electrode 5063 and is patterned. Thepixel electrode 5063 is overlapped on the connection wiring 5062 incontact therewith. It is also allowable to use a transparentelectrically conducting film by mixing 2 to 20 [%] of zinc oxide (ZnO)into indium oxide. The pixel electrode 5063 serves as an anode of the ELelement (FIG. 6(A)). When the area of the wiring region increasesrelative to the area of the pixel electrode, error increases due to arelation of detection. It is therefore desired that the ratio of pixelarea is large. Besides, the display element requires a high numericalaperture, and the requirements of the two are in agreement.

[0106] After formed up to this point, the element substrate is inspectedby using the inspection method and the inspection device of theinvention as described in the Example of the invention. FIG. 7(A) is atop view and FIG. 7(B) is a circuit diagram of the pixel portion of thelight-emitting device formed up to this point according to the Example.Common reference numerals are used in FIGS. 7(A) and 7(B).

[0107] The source of a switching TFT 702 is connected to a source wiring715, and the drain region is connected to a drain wiring 705. The drainwiring 705 is electrically connected to a gate electrode 707 of acurrent control TFT 706. Further, the source of the current control TFT706 is electrically connected to a current feeder line 716, and thedrain region is electrically connected to a drain wiring 717. The drainwiring 717 is further electrically connected to a pixel electrode(anode) 718 indicated by a dotted line.

[0108] Here, a holding capacity is formed in a region designated at 719.The holding capacity 719 is formed among a semiconductor film 720electrically connected to the current feeder line 716, an insulatingfilm (not shown) of the same layer as the gate-insulating film and thegate electrode 707. It is also possible to use, as a holding capacity,the capacity formed by the gate electrode 707, a layer (not shown) sameas the first interlayer-insulating film and the current feeder line 716.

[0109]FIG. 8 is a top view of the opposing detector substrate used inthe Example. The opposing detector substrate in this Example may use aglass or quartz as a material that permits electromagnetic waves toeasily pass through. Further, this Example uses a soft X-ray ofelectromagnetic waves of wavelengths of from 0.1 to 100 nm. The opposingdetector substrate can be fabricated by using the same method as the onefor fabricating the element substrate described in Example. Here,however, the opposing detector electrode formed on the opposing detectorsubstrate is formed of beryllium or aluminum which is different from thematerial forming the pixel electrodes of the element substrate, andshould permit soft X-rays to easily pass through. These materials may beformed on the whole surface of the opposing portions, or may be formedlike stripes or like a mesh.

[0110] When the opposing detector substrate is formed by anotherlow-temperature film-forming process, there can be used an organic resinsuch as vinyl chloride or acrylic resin in addition to glass and quartz.

[0111] Reference numeral 801 denotes an inspection TFT. The sourceregion 802 of the inspection TFT 801 is connected to the opposingdetector electrode through a source wiring 803, and is electricallyconnected to the pixel electrode of the element substrate when the gasin the air is irradiated with the soft X-rays to form an electricpassage. Further, the drain region 804 of the inspection TFT 801 isconnected to the drain wirings (805 a and 805 b), and is electricallyconnected to an ammeter (not shown) provided on the outer side.

[0112] The gas is ionized upon being irradiated with the soft X-rays. Inthis invention, the ionization stands for the one that is ionized tosuch an extent that a current flows from the pixel electrode to theopposing detector electrode through the ionized gas.

[0113] The gate electrode 806 is connected to the gate line 807, and theopposing detector electrode is a region indicated by a dotted line 808.

[0114] The element substrate having the pixel electrode is formed andis, then, inspected in a manner as described below. First, the elementsubstrate 901 and the opposing detector substrate 902 are arranged upand down as shown in FIG. 9 to carry out the inspection. In thisembodiment, the element substrate 901 and the opposing detectorsubstrate 902 are arranged in a manner as shown in FIG. 9, and theelectromagnetic waves are radiated from the upper side of the opposingdetector substrate to ionize the air. The invention, however, is in noway limited thereto only but may be such that the air is ionized to forman electric passage to flow an electric current between the elementsubstrate 901 and the opposing detector substrate 902.

[0115] When the opposing detector substrate 902 is irradiated with thesoft X-rays from the source 903 of electromagnetic waves, the softX-rays pass through the opposing detector substrate 902, and the airbetween the opposing detector substrate 902 and the element substrate901 is irradiated with the soft X-rays. In FIG. 9, the air is ionized bythe soft X-rays, and there is formed an apparent resistance asdesignated at 907.

[0116] Thus, an electric passage is formed in the air. When a videosignal is input to the selected pixel on the element substrate 901,therefore, a current flowing into the pixel electrode 904 also flowsinto the opposing detector electrode 905 on the opposing detectorsubstrate 902 passing through the electric passage.

[0117] The current, then, flows into an external ammeter 906 through thedrain wiring from the source region of the inspecting TFT connected tothe opposing detector electrode 905 via the drain region. Currentsflowing into the pixel electrode are detected by the external ammeter atthe time when the video signal is input (white) to the pixel on theelement substrate 901 and when no video signal is input thereto (black),and are expressed as a ratio of white and black to evaluate the qualityof TFT on the element substrate 901. The process for forming the ELelement is conducted while removing those devices of qualities lowerthan a reference value. Depending upon the cause of defect and thedegree of defect, further, the devices may be repaired through arepairing step and may be returned back to the subsequent steps.

[0118] Referring next to FIG. 6(B), the insulating film containingsilicon (silicon oxide film in this embodiment) is formed maintaining athickness of 500 [nm], an opening is formed at a position correspondingto the pixel electrode 5063, and a third interlayer-insulating film 5065is formed to serve as a bank. The opening is formed by the wet etchingmethod thereby to easily form the tapered side walls. Attention must begiven to that unless the side walls of the opening portion are formedsufficiently mildly, the EL layer is deteriorated to a conspicuousdegree due to a step.

[0119] Next, the EL layer 5066 and the cathode (MgAg electrode) 5067 arecontinuously formed by the, vacuum evaporation method without beingexposed to the open air. Here, the EL layer 5066 should have a thicknessof 80 to 200 [nm](typically, 100 to 120 [nm]) and the cathode 5067should have a thickness of 180 to 300 [nm](typically, 200 to 250 [nm]).

[0120] At this step, there are successively formed the EL layer 5066 andthe cathode 5067 for the pixel corresponding to red color, for the pixelcorresponding to green color and for the pixel corresponding to bluecolor. Here, however, the EL layer 5066 has a poor resistance againstthe solution and must be separately formed for each of the colorswithout relying upon the photolithography technology. It is thereforedesired to employ a method such as evaporation method of selectivelyforming the EL layer 5066 and the cathode 5067 on the required portionsonly while concealing the areas except the desired pixels by using ametal mask.

[0121] First, a mask is set to conceal all areas except the pixelscorresponding to red color, and the EL layer 5066 that emits red lightis selectively formed by using the mask. Next, a mask is set to concealall areas except the pixels corresponding to green color, and the ELlayer that emits green light is selectively formed by using the mask.Then, a mask is set to conceal all areas except the pixels correspondingto blue color, and the EL layer that emits blue light is selectivelyformed by using the mask. Though different masks were used above, it isalso allowable to use the same mask.

[0122] Though in the foregoing was used the system for forming ELelements of three kinds corresponding to RGB, there may be used a systemcombining a white light-emitting EL element and a color filter, a systemcombining a blue light-emitting or green light-emitting EL element and afluorescent material (fluorescent color conversion layer: CCM) or asystem using a transparent electrode as the cathode (opposing electrode)and overlapping thereon EL elements corresponding to RGB.

[0123] Known materials can be used for forming the EL layer 5066. As theknown material, there can be preferably used an organic material bytaking the drive voltage into consideration. For example, four layerscomprising a positive hole-injection layer, a positive hole-transportinglayer, a light-emitting layer and an electron injection layer may beused as the EL layer.

[0124] Next, an opposing electrode 5067 is formed by using a metal maskon the pixels (pixels of the same line) having switching TFTs of whichthe gate electrodes are connected to the same gate signal line. ThoughMgAg which is a cathode material was used for the opposing electrode5067 in this Example, it should be noted that the invention is notlimited thereto only, but any other known material may be used as theopposing electrode 5067.

[0125] Finally, a passivation film 5068 which is a silicon nitride filmis formed maintaining a thickness of 300 [nm]. Upon forming thepassivation film 5068, the EL layer 5066 is protected from the moistureso as to exhibit further improved reliability of EL elements.

[0126] Thus, the light-emitting device of a structure shown in FIG. 6(B)is completed. In the step of forming the light-emitting device accordingto this Example, the source signal lines are formed by using Ta and Wwhich are the materials forming the gate electrodes, and the gate signallines are formed by using Al which is a wiring material forming thedrain electrodes due to the circuit constitution and the steps. It is,however, allowable to use different materials, too.

[0127] Upon arranging TFTs of an optimum structure not only in the pixelportion but also in the drive circuit portion, the light-emitting deviceof this Example exhibits a very high reliability and improved operationcharacteristics. In the step of crystallization, further, it is alsoallowable to add a metal catalyst such as Ni to enhance thecrystallinity. This enables the source signal line drive circuit tooperate at a drive frequency of not lower than 10 [MHz].

[0128] First, in order to prevent the drop in the operation speed asmuch as possible, the TFT of a structure which suppresses the injectionof hot carriers is used as the n-channel TFT for the CMOS circuit thatforms the drive circuit portion. The drive circuit referred to hereincludes shift registers, buffers, and level shifters, and includeslatches in the line sequential drive and includes transmission gates inthe point sequential drive.

[0129] In the case of this Example, the active layer of the n-channelTFT includes—the source region, drain region, overlapped LDD region(L_(OV) region) overlapped on the gate electrode with thegate-insulating film sandwiched therebetween, an offset LDD region(L_(OFF) region) which is not overlapped on the gate electrode with thegate-insulating film sandwiched therebetween, and channel-formingregion.

[0130] The p-channel TFT of the CMOS circuit needs not be particularlyprovided with the LDD region since it is not almost deteriorated by theinjection of hot carriers. It is, of course, allowable to provide theLDD region like the N-channel TFT to cope with the hot carriers.

[0131] Further, when the drive circuit employs the CMOS circuit in whichthe current flows in both directions through the channel-forming region,i.e., employs the CMOS circuit in which the roles of the source regionand of the drain region are replaced by each other, it is desired thatthe n-channel TFT forming the CMOS circuit forms the LDD regions on bothsides of the channel-forming region in such a manner that the LDDregions sandwich the channel-forming region. Such an example can berepresented by a transmission gate used for the point sequential drive.Further, when the drive circuit employs the CMOS circuit which mustsuppress the off current as small as possible, it is desired that then-channel TFT forming the CMOS circuit has the L_(OV) region. This canalso be exemplified by the transmission gate used for the pointsequential drive.

[0132] In practice, further, when the device is completed up to thestate of FIG. 6(B), it is desired to package (seal) the device with aprotection film (laminate film, etc.) having high air-tightnesspermitting the gas to escape little or with a light-transmitting sealingmember so that the device will not be exposed to the open air. In thiscase, the interior of the sealing member may be filled with an inertatmosphere or a hygroscopic material (e.g., barium oxide) may bearranged therein to improve the reliability of the EL element.

[0133] After the sir-tightness is enhanced by the treatment such aspackaging, the device is completed as the product by attaching aconnector (flexible printed circuit: FPC) for connecting the elementformed on the substrate or for connecting the terminals drawn from thecircuit to the external signal terminals. The device in a state that canbe shipped is called light-emitting device in this specification.

EXAMPLE 2

[0134] Next, described below with reference to FIG. 10 is the structureof the pixel portion of the element substrate for conducting theinspection according to the invention, which is different from thestructure of Example 1.

[0135] A pixel portion 1001 includes source signal lines (S1 to Sx)connected to the source signal line drive circuit, current feeder lines(V1 to Vx) connected to an external power source of the light-emittingdevice via the FPC, gate signal lines (first gate signal lines)(Ga1 toGay) for writing connected to the write gate signal line drive circuit,and gate signal lines (second gate signal lines)(Ge1 to Gey) for erasingconnected to the erase gate signal line drive circuit.

[0136] A pixel 1005 is formed by a region that includes source signallines (S1 to Sx), current feeder lines (V1 to Vx), write gate signallines (Ga1 to Gay) and erase gate signal lines (Ge1 to Gey). In thepixel portion 1001 are arranged plural pixels 1005 like a matrix. Theelement substrate of this Example can be put into practice incombination with the constitution of Example 1.

EXAMPLE 3

[0137] Described below with reference to FIG. 11 is a method ofinspection by using an opposing detector substrate different from theone dealt with in Example 1 for conducting the inspection according tothe invention.

[0138] In FIG. 11, reference numeral 1101 is a source of electromagneticwaves for generating soft X-rays having wavelengths of 0.1 to 100 nmamong the electromagnetic waves, and a power source 1104 is connected tothe source 1101 of electromagnetic waves.

[0139] The soft X-rays emitted from the source 1101 of electromagneticwaves fall on the opposing detector substrate 1102 passing through afine hole of a shielding plate 1105 corresponding to the object surface.Other portions are shielded by the shielding plate 1105. The shieldingplate 1105 is made of a material capable of shielding the soft X-rays toa sufficient degree. The soft X-rays pass through the opposing detectorsubstrate 1102 and fall on the air between the opposing detectorsubstrate 1102 and the element substrate 1103. Unlike the opposingdetector substrate 1102 on which the inspection TFT and the opposingdetector electrode are formed for each of the opposing portions formedlike a matrix used in Example 1, the opposing detector substrate 1102used in this Example has an electrically conducting film such as of ametal formed on the insulator so that the whole surface works as theopposing detector electrode. The electrically conducting film needs notbe formed on the whole surface but may be formed in the form of stripesor a mesh.

[0140] The opposing detector substrate 1102 can be placed on the elementsubstrate 1103 to conduct the inspection.

[0141] As the conductor for forming the opposing detector electrode,there can be used a metal material which permits the soft X-rays to passthrough highly efficiently, such as beryllium or aluminum. The shieldingplate 1105 may be the one that shields the soft X-rays. For example,there may be used a material which permits the soft X-rays to passthrough little, such as lead glass having a hole perforated in a portionthrough where the soft X-rays are to be passed for irradiation.

[0142] In this Example, the opposing detector substrate 1102 and theelement substrate 1103 positioned under the source 1101 ofelectromagnetic waves and shielding plate 1105, are shifted together toirradiate the air present between the opposing detector substrate 1102and the element substrate 1103 with the soft X-rays. That is, theelement substrate 1103 is interlocked to the opposing detector substrate1102.

[0143] As the air present between the opposing detector substrate 1102and the element substrate 1103 is irradiated with the soft X-rays thathave passed through the opposing detector substrate 1102, an electricpassage is formed between the opposing detector substrate 1102 and theelement substrate 1103, making it possible to measure the current thatflows from the pixel electrode possessed by the pixel formed on theelement substrate 1103 to the opposing detector electrode formed on theopposing detector substrate 1102.

[0144] Though in the foregoing was described the constitution forinspecting the element substrate by interlocking the opposing detectorsubstrate 1102 and the element substrate 1103 together, it is alsoallowable to fix them and move the source of electromagnetic waves only.

[0145] The measuring method and the evaluation method may comply withthose of Example 1. The constitution of this embodiment can be executedupon combining the constitutions of Examples 1 and 2.

EXAMPLE 4

[0146] Described below with reference to FIG. 12 is a method ofinspection by using an opposing detector substrate different from thosedealt with in Examples 1 and 3 in conducting the inspection according tothe invention.

[0147] In FIG. 12, reference numeral 1201 denotes a source ofelectromagnetic waves for generating X-rays having wavelengths of 0.01to 100 nm among the electromagnetic waves, and a power source 1204 isconnected to the source 1201 of electromagnetic waves.

[0148] The X-rays emitted from the source 1201 of electromagnetic wavesare focused on the opposing detector substrate 1202 and falls on theelement substrate 1203 passing through the opposing detector substrate1202. Here, the material used for the opposing detector electrode formedon the opposing detector substrate 1202 may be beryllium or aluminumthat permits X-rays to pass through highly efficiently.

[0149] In this Example, the element substrate 1203 is provided under thesource 1201 of electromagnetic waves and the opposing detector substrate1202, and is moved every time when each of the pixels of the elementsubstrate 1203 is inspected. The mirror 1205 works to focus the X-rays.That is, in this Example, the source 1201 of electromagnetic waves andthe opposing detector substrate 1202 are fixed, and the elementsubstrate 1203 is moved every time when a different pixel is inspected.

[0150] As the air present between the opposing detector substrate 1202and the element substrate 1203 is irradiated with the X-rays, anelectric passage is formed between the opposing detector substrate 1202and the element substrate 1203, making it possible to measure thecurrent that flows from the pixel electrode possessed by the pixelformed on the element substrate 1203 to the opposing detector electrodeformed on the opposing detector substrate 1202. In this embodiment, theX-rays that have passed through the opposing detector substrate 1202fall on the pixel that is to be measured on the element substrate 1203forming an electric passage at a desired position and making it possibleto more correctly measure the current.

[0151] In the foregoing was described the constitution for moving theelement substrate 1203. It is, however, also allowable to conduct theinspection by securing the element substrate 1203 and by interlockingthe source 1201 of electromagnetic waves and the opposing detectorsubstrate 1202 together. Further, the opposing detector substrate 1202may be formed like a ring to permit the passage of the X-rays, or anelectrode may be simply provided in the vicinity thereof.

[0152] In this Example, the measuring method and the evaluation methodare the same as those of Example 1. When it is difficult to focus theX-ray, however, a mirror having a high reflection factor is providedalong the periphery as required or a capillary plate is provided so thatthe X-ray can be projected onto a desired position. It is furtherdesired that the distance is as close as possible between the opposingdetector substrate 1202 and the element substrate 1203. The constitutionof this Example can be put into practice being freely combined with theconstitutions of Examples 1 to 3.

EXAMPLE 5

[0153] Examples 1 to 4 have dealt with the substrates on which the TFTswere formed as element substrates. The invention, however, can be putinto practice even by using MOS transistors formed on the semiconductorsubstrate instead of the TFTS. For example, the semiconductor substrate(typically, a silicon wafer) on which the MOS transistors are formed canbe inspected as the element substrate.

[0154] According to this Example, the element substrate can be inspectedby any one of the Examples of the invention, the inspection method ofExample 3 or the inspection method of Example 4.

EXAMPLE 6

[0155] Described below with reference to FIGS. 15 and 16 are the caseswhere a connector such as FPC or TAB is connected to the display panelof the invention to ship it as a product.

[0156] In FIG. 15, reference numeral 1801 denotes a pixel portion thathas passed the inspection method of the invention, and that is providedwith plural pixels.

[0157] Reference numeral 1802 denotes a source signal line drivecircuit, and 1803 denotes a gate signal line drive circuit. In responseto selection signals output from the gate signal line drive circuit1803, video signals output from the source signal line drive circuit1802 are input to the specified pixels of the pixel portion 1801. Thevideo signals may be either digital signals or analog signals. Further,the source signal line drive circuit 1802 and the gate signal line drivecircuit 1803 may be provided in any number.

[0158] In this specification, an OLED panel 1807 refers to a module thatincludes a drive circuit constituted by the source signal line drivecircuit 1802 and the gate signal line drive circuit 1803, the pixelportion 1801, and a connector for connecting the wiring possessed by thepixel portion 1801 and for connecting the wiring possessed by the drivecircuit to an external unit. The OLED panel 1807 needs not necessarilybe provided with the drive circuit, and the pixel portion 1801 and thewiring possessed by the pixel portion 1801 may be separately formed.

[0159] Here, the OLED panel in which the drive circuit and the pixelportion 1801 are provided on the separate substrates and are connectedtogether by a connector such as FPC or TAB, is called an OLED panel ofthe externally attached type, and the OLED panel in which the drivecircuit and the pixel portion 1801 are provided on the same substrate iscalled an OLED panel of the integral type. FIG. 16(A) shows an OLEDpanel of the externally attached type, and FIG. 16(B) shows an OLEDpanel of the integral type.

[0160]FIG. 16(A) is a top view of the OLED panel of the externallyattached type. The pixel portion 1801 is provided on the substrate 1810,and the wirings possessed by the pixel portion 1801 are connected to thesource signal line drive circuit 1802 and to the gate signal line drivecircuit 1803 formed on the substrate 1812 for external attachment viaFPCs 1811. Wirings of the source signal line drive circuit 1802, of thegate signal line drive circuit 1803 and of the pixel portion 1801 areconnected to an external unit through the FPC 1812 for externalconnection.

[0161]FIG. 16(B) is a top view of the OLED panel of the integral type.On the substrate 1810 are provided the pixel portion 1801, source signalline drive circuit 1802 and gate signal line drive circuit 1803. Thewirings of the pixel portion 1801, of the source signal line drivecircuit 1802 and of the gate signal line drive circuit 1803 areconnected to an external unit through the FPCs 1812 for externalconnection.

[0162] In FIG. 15, reference numeral 1804 denotes a controller having afunction for driving the drive circuit and for displaying an image onthe pixel portion 1801. The controller 1804 works to send signalscontaining image data input from an external unit to the source signalline drive circuit 1802, to form signals (e.g., clock signals (CLK),start pulse signal (SP)) for driving the drive circuit, and works as apower source for feeding a potential to the drive circuit and to thepixel portion 1801.

[0163] In this specification, an OLED module 1808 refers to a modulethat includes the drive circuit, pixel portion 1801, controller 1804,pixel portion 1801, drive circuit, controller, and connectors forconnecting the wirings thereof to the external unit. The OLED module1808 is the one in which the OLED panel 1807 is provided with the drivecircuit and the controller 1804.

[0164] Reference numeral 1805 denotes a microcomputer for controllingthe controller 1804. In this specification, the module including themicrocomputer 1805 and the OLED module 1808 is called OLED module 1809with microcomputer.

[0165] In practice, the OLED panel 1807, the OLED module 1808 and theOLED module 1809 with microcomputer are shipped as products. In thisspecification, the OLED panel 1807, OLED module 1808 and OLED module1809 with microcomputer are all regarded as light-emitting devices.

[0166] The light-emitting device of this Example can employ the methodof fabrication and inspection method dealt with in Example 1 and canfurther employ the constitution of pixel portion same as that of Example2. The device can be further inspected by the inspection methoddescribed in Example 3 or 4, and to which can be applied the elementsubstrate of Example 5.

EXAMPLE 7

[0167] The invention can be put into practice even when plural elementsubstrates are to be simultaneously formed on a large substrate.

[0168] In this case, the drive circuit formed separately from theelement substrate, the opposing detector substrate and source ofelectromagnetic waves may be interlocked together and may be moved on tothe element substrate that is to be inspected. Further, the elementsubstrate only may be moved to conduct the inspection.

[0169] In inspecting plural element substrates, the electric connectionmust be made again between the element substrate to be inspected and thedrive circuit for every inspection. The connection terminals on the sideof the element substrate used in this case may include terminals forinspection. It is, however, also allowable to use terminals that arefinally connected to the external unit through the FPC.

EXAMPLE 8

[0170] A light-emitting device formed by implementing examination methodof the present invention has superior visibility in bright locations incomparison to a liquid crystal display device because it is aself-emission type device, and moreover its field of vision is wide.Accordingly, it can be used as a display portion for various electronicdevices. For example, it is appropriate to use the light-emitting deviceformed by implementing the examination method of the present inventionas a display portion of a display having a diagonal equal to 30 inchesor greater (typically equal to 40 inches or greater) for appreciation ofTV broadcasts by large screen.

[0171] Note that all displays exhibiting (displaying) information suchas a personal computer display, a TV broadcast reception display, or anadvertisement display are included as the light-emitting device.Further, the light-emitting device using the examination method of thepresent invention can be used as a display portion of the other variouselectronic devices.

[0172] The following can be given as examples of such electronic devicesof the present invention: a video camera; a digital camera; a goggletype display (head mounted display); a navigation system; an audioreproducing device (such as a car audio system, an audio compo system);a notebook personal computer; a game equipment; a portable informationterminal (such as a mobile computer, a mobile telephone, a mobile gameequipment or an electronic book); and an image playback device providedwith a recording medium (specifically, a device which performs playbackof a recording medium and is provided with a display which can displaythose images, such as a digital video disk (DVD)). In particular,because portable information terminals are often viewed from a diagonaldirection, the wideness of the field of vision is regarded as veryimportant. Thus, it is preferable that the light-emitting device isemployed. Examples of these electronic devices are shown in FIGS. 13 and14.

[0173]FIG. 13A is a display for displaying, containing a casing 1301, asupport stand 1302, and a display portion 1303. The light-emittingdevice which is applied the examination method of the present inventioncan be used in the display portion 1303. Since the light-emitting is aself-emission type device with no need of a back light, its displayportion can be made thinner than a liquid crystal display device.

[0174]FIG. 13B is a video camera, containing a main body 1311, a displayportion 1312, an audio input portion 1313, operation switches 1314, abattery 1315, and an image receiving portion 1316. The light-emittingdevice which is applied to the examination method of the presentinvention can be used in the display portion 1312.

[0175]FIG. 13C is a portion of a head mounted type electrical appliance(right side), containing a main body 1321, a signal cable 1322, a headfixing band 1323, a screen portion 1324, an optical system 1325, and adisplay portion 1326. The light-emitting device which is applied theexamination method of the present invention can be used in the displayportion 1326.

[0176]FIG. 13D is an image playback device (specifically, a DVD playbackdevice) provided with a recording medium, containing a main body 1331, arecording medium (such as a DVD) 1332, operation switches 1333, adisplay portion (a) 1334, and a display portion (b) 1335. The displayportion (a) 1334 is mainly used for displaying image information, andthe display portion (b) 1335 is mainly used for displaying characterinformation, and the light-emitting device which is applied to theexamination method of the present invention can be used in the displayportion (a) 1334 and in the display portion (b) 1335. Note that domesticgame equipment is included as the image playback device provided with arecording medium.

[0177]FIG. 13E is a goggle type display device (head mounted display),containing a main body 1341, a display portion 1342, and arm portion1343. The light-emitting device which is applied the examination methodof the present invention can be used in the display portion 1342.

[0178]FIG. 13F is a personal computer, containing a main body 1351, acasing 1352, a display portion 1353, and a keyboard 1354. Thelight-emitting device which is applied the examination method of thepresent invention can be used in the display portion 1353.

[0179] Note that if the emission luminance of EL materials becomeshigher in the future, it will be possible to use the light-emittingdevice of the present invention in a front type or a rear type projectorby projecting light including output images, which can be enlarged bylenses or the like.

[0180] The above electrical appliances are becoming more often used todisplay information provided through an electronic telecommunicationline such as the Internet or CATV (cable television), and in particular,opportunities for displaying animation information are increasing. Theresponse speed of EL materials is extremely high, and therefore thelight-emitting device is favorable for performing animation display.

[0181] Since the light emitting portion of the light-emitting deviceconsumes power, it is preferable to display information so as to havethe emitting portion become as small as possible. Therefore, when usingthe light-emitting device in a display portion which mainly displayscharacter information, such as a portable information terminal, inparticular, a portable telephone and an audio reproducing device, it ispreferable to drive it by setting non-emitting portions as backgroundand forming character information in emitting portions.

[0182]FIG. 14A is a portable telephone, containing a main body 1401, anaudio output portion 1402, an audio input portion 1403, a displayportion 1404, operation switches 1405, and an antenna 1406. Thelight-emitting device of the present invention can be used in thedisplay portion 1404. Note that by displaying white characters in ablack background in the display portion 1404, the power consumption ofthe portable telephone can be reduced. Further, in the case whereperiphery is dark, it is effective that the power consumption can bereduced by decreasing the applied voltage, thereby lowering luminance.

[0183]FIG. 14B is an audio reproducing device, specifically a car audiosystem, containing a main body 1411, a display portion 1412, andoperation switches 1413 and 1414. The light-emitting device of thepresent invention can be used in the display portion 1412. Furthermore,an audio reproducing device for a car is shown in Embodiment 8, but itmay also be used for a portable type and a domestic type of audioreproducing device. Note that by displaying white characters in a blackbackground in the display portion 1412, the power consumption can bereduced. This is particularly effective in a portable type audioreproducing device.

[0184]FIG. 14C is a digital camera, containing a main body 1421, adisplay portion (A) 1422, an eye piece portion 1423, an operation switch1424, a display portion (B) 1425 and a battery 1426. The EL displaydevice which is applied the examination method of the present inventioncan be used in the display portion (A) 1422 and the display portion (B)1425. Note that in the case of using mainly the display portion (B) 1425as an operation panel, by displaying white characters in a blackbackground, the power consumption of the digital camera can be reduced.

[0185] In the case of electrical appliances shown in this embodiment,the sensor portion is provided to perceive the external light and thefunction to lower the brightness of display when it is used in the darkarea as a method to lower the power consumption.

[0186] The range of applications of the present invention is thusextremely wide, and it is possible to apply the present invention toelectrical appliances in all fields. Furthermore, Embodiment 8 can beimplemented in combination of any structures of the Embodiments 1 to 7.

[0187] The inspection method of the invention makes it possible todistinguish whether the element substrate is acceptable or defectiveeven without completing the element substrate as a light-emitting deviceor without really effecting the display and, hence, to remove thedefective device from the subsequent production process. Accordingly,the cost of production is decreased and the yield is improved.

1. A device for inspecting element substrates comprising a source ofelectromagnetic waves and an opposing detector substrate, the source ofelectromagnetic waves ionizing a gas present between the opposingdetector substrate and an element substrate that is to be inspected. 2.A device according to claim 1, wherein the source of electromagneticwaves generates electromagnetic waves or X-rays of a wavelength of from0.01 to 100 nm.
 3. A device according to claim 1, further comprisingmeans for measuring an electric current between the opposing detectorsubstrate and the element substrate.
 4. A device according to claim 1,wherein the opposing detector substrate has an opposing detectorelectrode.
 5. A device according to claim 4, wherein the opposingdetector electrode is made of a conductor that permits the transmissionof electromagnetic waves or X-rays of a wavelength of 0.01 to 100 nm. 6.A device according to claim 5, wherein the opposing detector electrodeis made of beryllium or aluminum.
 7. A device according to claim 1,wherein the opposing detector substrate has plural TFTs and pluralelectrodes connected to the TFTs.
 8. A device according to claim 1,further comprising means for so moving the element substrate that thedistance becomes the shortest between the source of electromagneticwaves and the to-be-detected position on the element substrate.
 9. Adevice according to claim 1, further comprising means for so moving theopposing detector substrate and the element substrate that the distancebecomes the shortest among the source of electromagnetic waves, theto-be-detected position on the element substrate and the correspondingposition of the opposing detector electrode.
 10. A method of inspectingelement substrates by measuring an electric current between the elementsubstrate and an opposing detector substrate by using a device accordingto claim 1, thereby to inspect the current-flowing state of the pixelelectrodes of the element substrate.
 11. A method of inspecting elementsubstrates by emitting electromagnetic waves from a source ofelectromagnetic waves in order to ionize a gas between the opposingdetector substrate and the element substrate to be inspected.
 12. Amethod according to claim 11, wherein the source of electromagneticwaves generates electromagnetic waves or X-rays of a wavelength of 0.01to 100 nm.
 13. A method according to claim 11, wherein a current ismeasured between the opposing detector substrate and the elementsubstrate.
 14. A method according to claim 11, wherein the elementsubstrate is so moved that the distance becomes the shortest between thesource of electromagnetic waves and the to-be-detected position on theelement substrate.
 15. A method according to claim 11, wherein theopposing detector substrate and the element substrate are so moved thatthe distance becomes the shortest among the source of electromagneticwaves, the to-be-detected position on the element substrate and thecorresponding position of the opposing detector electrode.